Urea in milk

The next group of multimembrane systems comprises membranes sensitized biologically using immobilized enzymes or microorganisms. Species that are directly sensed by an ISE are produced in the enzymatic reaction of the analyte. Examples of such sensors are those used for determination of urea in milk, based on immobilized urease and measurement of a pH change. An example of the application of bacteria strains is the use of immobilized recombinant Escherichia coli coupled with a pH electrode. Such electrodes have been used for determination of cephalosporins. When this bacterial strain is coupled with a CO2 gas sensor, glutamic acid determination can be carried out. 

Spectroscopic, luminescence, turbidimetric, and electrochemical methods of detection have been combined with SIA for the successful determination of amino acids, sugars, and trace elements in matrices such as meats, vegetables, breads, wines, juices, and milks. Many of these methodologies required sample pretreatment and whilst most performed this in an offline manner there have been some reports of online sample cleanup. Microwave assisted digestion was performed in-line for the determination of phosphorous, calcium, magnesium, and iron in slurried foodstuffs, wine, milk, and soft drinks whilst gaseous diffusion allowed interference removal for the determination of urea in milk. 

Immimodiagnostics and enzyme biosensors are two of the leading technologies that have a greatest impact on the food industry. The use of these two systems has reduced the time for detection of pathogens such as Salmonella to 24 hr and has provided detection of biological compounds such as cholesterol or chymotrypsin [15]. Biosensors analyses Beta lactams in milk and presence of urea in milk that lead to production of synthetic milk, the biocomponent part of the urea biosensor is an immobilized urease yielding bacterial cell biomass isolated from soil and is coupled to the ammonium ions selective electrodes of a potentiometric transducer. The membrane potential of all types of potentiometric cell based probes is related to the activity of electrochemically-detected product [16]. 

The original electrode was developed for detecting urea in blood and urine samples. An enzyme sensor for measuring urea in milk has been reported by an Indian group [31]. The working principle is identical to that of Guilbault s sensor. The sensor prepared for milk analysis, however, is a flat cell fabricated with screen-printed technology. 

Czaudema, M. and K. Kowalczyk, 2009. Easy and accurate determination of urea in milk, blood plasma, urine and selected diets of mammals by high-performance liquid chromatography with photodiode array detection preceded by pre-column derivatization. Chem. Anal. 54, 919-937. 

Frank, B. and C. Swensson, 2002. Relationship between content of crude protein in rations for dairy cows and milk yield, concentration of urea in milk and ammonia emissions. J. Dairy Sci. 85, 1829-1838. 

Branched chain fatty acids are present in milk (Kurtz 1974 Patton and Jensen 1976), and the following have been identified monomethyl 11-24 13-19, three or more positional isomers and multimethyl 16-28. Iverson (1983) and Iverson et al. (1965) identified the branched and other acids with the aid of urea fractionation. Saturated n-fatty acids of longer chain length form inclusion complexes with urea more readily than acyls with functional groups. The branched chain fatty acids do not form adducts. 

Effect of Urea on the Distribution of 14C-Methyl-/ -Lactoglobulin or 14C-Methyl-/c-Casein in Heated Milk. Muir and Sweetsur (25) exploited the interesting observations by Robertson and Dixon (26) that the heat stability of milk proteins is related to the urea level of the milk, and that adding relatively small amounts of urea increased the heat stability of milk (27). To examine the urea effect further, we added urea to milk containing either M-/3-L or M-k-C and measured the ultracentrifugal distribution of C-14 after heat treatment. The experiments using... 

Some methods which do not involve separation of the FFAs from the milk fat or the whole product have considerable appeal because of their simplicity. Sharma and Bindal (1987) exploited the property of methyl urea to complex triglycerides in producing methyl esters with BF3-methanol without first separating the FFAs from the fat, while Spangelo et al. (1986) were able to methylate FFAs in an acetonitrile extract of milk with methyl iodide in the presence of an anion exchange resin as catalyst. Miwa and Yamamoto (1990) derivatised the FFAs in milk and milk products for HPLC analysis by direct reaction with 2-nitrophenylhydrazine hydrochloride. 

IEF can also be carried out under denaturing conditions, for example in the presence of 9 M urea. For the analysis of hydrophobic proteins, non-ionic detergents such as Nonidet NP-40 or Triton X-100 can be added to the sample and the IEF gel. Analytical IEF is used to determine the pi of proteins, and also as a critical check of the homogeneity of protein preparations. The reprodudbility and resolving power of the technique is exploited in various applications where it is used to establish the identity and complexity of protein mixtures for example in food analysis, the origin of proteins in milk preparations, and in clinical analysis, determining the isoenzyme profile of apolipoproteins. 

Orotic Acid. l,2,3,6.Tetrahydro-2,6-dioxo-4-py-nmidinecartroxyhc acid uracil-6-carboxylic acid whey factor animal galactose factor Oropur Orotyl. CjH.N.O, mol wt 156.10. C 38.47%. H 2.58%, N 17.95%. O 41.00%. A pyrimidine precursor in animal organisms, found in milk Bachstez. Ber. 64, 2683 (1931) Hilbert, J. Am. Chem. Soc. 54, 2082 (1932) Johnson, Schroeder, ibid. 2942. Synthesis from aspartic acid Nye. Mitchell, ibid. 69, 1382 (1947). Prepn by condensation of urea with monoethyl ester of ox -alacetic acid in methanol Scriabine, U.S. pat. 2,937,175... 

R. Oltner, S. Bengtsson, and K. Larsson, Flow Injection Analysis for the Determination of Urea in Cow Milk. Acta Vet. Scand., 26 (1985) 396. 

One important amide is caramide (NH2CONH2), or urea, as it is commonly known. Urea is an end product in the metabolic breakdown of proteins in mammals. It is found in the blood, bile, milk, and perspiration of mammals. When proteins are broken down, amino groups (NH2) are removed from the amino acids. The amino groups are then converted to ammonia (NH3) that are toxic to the body. The toxic ammonia is converted to nontoxic urea in the liver. The urea is filtered out of the blood in the kidneys and passed from the body in urine. 

The level of urea infusion had no effect on DM, digestible OM or NDF intake or NDF digestibility (Table 1). Nitrogen intake from the basal diet was not affected by the treatment but urea infusions increased the total N intake (P<0.01), milk yield (P=0.0S) and milk protein yield (P=0.08) in a linear manner. As a response to urea infusions ruminal ammonia concentrations increased in a curvilinear manner because there were no effects at the lower levels (U1-U4) but at the highest level of urea infusion the ammonia concentration sharply increased. The responses observed in milk urea concentrations were not entirely consistent with those in ruminal ammonia because milk urea concentrations increased in a linear manner (P<0.01). In agreement with milk urea concentration... 

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